Question

What is the fate of the notochord in an adult organism which belongs to Gnathostomata?
A)Notochord extinct
B)Notochord is replaced by the vertebral column
C)Notochord becomes vestigial
D)Notochord continues same as in larval stage

Answer 1

Hint: Pisces are the members of Chordata phylum of the animal kingdom and the subphylum is Vertebrata, the Vertebrata is further categorised into Agnatha and the Gnathostomata, Pisces belong to the Gnathostomata group of the Vertebrata.

Complete answer:
The vertebrata are a subphylum under the phylum of Chordata. Further, the phylum Chordata is categorised into three subphyla namely Urochordata, Cephalochordata and Vertebrata. Vertebrata are further categorised into Agnatha and Gnathostomata.
Agnatha superclass that show involvement of class Cyclostomata in which the organisms do not bear jaws, Hagfishes and Lampreys are its good examples.
Gnathostomata have the presence of all organisms that bear true jaws. It is divided into superclass Pisces and Tetrapoda which are again divided into subgroups.

As we know that all vertebrates have observed to show the presence of notochord during their embryonic stages but the adults have a replacement of notochord with the bony or cartilaginous vertebral column.
1.This is a characteristic fact that the vertebrates have a characteristic feature of having a notochord and shows a presence of paired pharyngeal gill slits as well as the presence of an post-anal tail.
2.In the phylum Chordata there is the involvement of sub phylum in it such as vertebrates, hemichordates, cephalochordates, etc which clearly tells that the all vertebrates are chordates but it is always said all chordates are not vertebrates as other subphyla are also present.
3.Chordates not possessing vertebrates have one present in them.
So as Gnathostomata is a vertebral group the notochord is replaced by a vertebral column in adults.

Hence, the correct answer is option (B)

Note: It is should always be remember that notochord presence is the specialized feature of the chordates which tends to change in some subphylum and stays the same in other subphylums. Chordates are all the member that are known to occur in it whether urochordates, cephalochordates or vertebrates but vertebrates are only the members present in this subphylum.